my nephew did it to his cot and there was wood splinters, I suggested to my sister in law to wrap a large sheet or sarong around the rails to cover it. It worked for her but it looked funny

 Just a phase. Put some chew toys in the cot (make sure they are safe).  Most cots are safe to chew. Both my boys did this.

It's a phase.  For my 2nd child, it lasted from the time she got teeth until she turned 4, and it wasn't restricted to her chewing her cot either.  She actually chewed anything that was wood.

Our 3 year old took it up for a while too, though thankfully has stopped for now.  The youngest 2, well, they haven't reached that stage yet! lol.  And my oldest never did it.

The wood of the cot shouldn't cause any real problems.  Our cot, the wood fibres are just like the tough, chewy fibres found in the core of a pineapple, so no risk of splinters.  But, the cot is ruined from chewing, and not going to be handed on to other families when mine is done with it.

heres a thought i just had you know that nail polish to stop nail bitting it taste bad maybe you could paint some on where she chews the cot it may deture her.